Understanding Pressure

So essentially, yes velocity = pressure. Higher the pressure the more the velocity. Lower the pressure the lower the velocity. Only thing we’ve got to measure pressure is to judge by book velocity. Primer crater, head swipes, flatten primmer, can all show false pressures. And no signs doesn’t necessarily mean no high pressure either.
 
An old thread !

Need to be careful on the oversimplification of MUZ-V == PSI.

To illustrate, some powders will give a spike of pressure, above max PSI,
while other powders will give a safe smoothed mound of pressure for same MUZ-V.

A handy tool to see examples of estimated pressure curve shape is Quickload.
 
JMette, I can not agree with your assessments here. Velocity is a result, and while some correlation exists, correlation does not imply or equal causation.

Especially in this case, because as Bob Atl said, pressure is pressure, and is not velocity specific in any instance. This is easily evidenced by the same loads being able to produce 100fps more or 100fps less in different barrels. So while velocity will be a metric for the median, to either side of the median is danger.

 
Every thing you need to now about pressure. To much can blow up any rifle and do a lot of damage to you. Doesn't matter what the pressure is as the overwhelming majority of us have no means to measure it. That mean's pressure is just a number! What is important is to learn to recognize pressure sign's and how to avoid them. Then suddenly the number means nothing anymore because you'll never know what your getting in the first place. What you need to know is how to recognize dangerous pressure when you see it!
 
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Here are a couple of things to consider regarding pressure in addition to the excellent article from Primal Rights.

1) Case expansion. By measuring your cases above the web, you can track expansion as a result of pressure. Case expansion can be normal especially in short cases like the 6BR where the die isn't sizing the entire length of a case. Over time this leads to "clicky" bolt. A sign that the case is hard to pull out by the extractor. Rifles are all different so signs like ejector wipe may not appear as serious from rifle to rifle. Measuring case expansion can give you an objective way to detect pressure. Small body dies can be used to size the brass prior to full length resizing if you have "expanded" a few cases with a high pressure load. Case heads with wipe signs don't clean up as easy and hang around potentially leading people to believe they still have high pressure.

2) Pierced primers. Primers can be pierced by over pressure loads certainly but can also be pierced by bolts with large firing pin holes and small firing pins. Savage bolts are often built with small diameter pins and large holes. If your cartridge has small primers this can easily occur. Best remedy is to have the bolt "bushed" where the firing pin hole is reduced. I had this problem with a new to me used rifle that was piercing low pressure loads. I even tested some factory ammo to be add another data point. Sent the bolt to a pro to get bushed, problem solved.

"The more you know"...
 
Wish I would have had this around when I started reloading when I was in college. Would have made me a little less skiddish with loading to the point I could really utilize the brass through its entire life. Great article!
 
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